In recent years, for the purpose of improving performance of internal combustion engines in terms of gas mileage and output power etc., technologies that enable to vary the compression ratio of internal combustion engines nave been proposed. For example, there has been disclosed a technology in which the cylinder block, which is an engine component that constitutes a combustion chamber of an internal combustion engine, and the crankcase are displaced relative to each other by rotationally driving a control shaft coupled to the cylinder block and the crankcase, thereby changing the volume of the combustion chamber to vary the compression ratio of the internal combustion engine (see, for example, Japanese Patent Application Laid-Open No. 2003-206771).
In another disclosed technology concerning an internal combustion engine in which the compression ratio of the internal combustion engine can be varied by swinging the cylinder block relative to the crankcase, a gear case and auxiliary machines are mounted on a side wall provided on the crankcase to simplify the mounting process while utilizing a conventional type flange surface (see, for example, Japanese Patent No. 3224816).